1. Field of the Invention
The present invention relates to paving machines which insert dowel bars into the new concrete pavement.
2. Description of Related Art
Over the years, various designs for paving machines which insert dowel bars have been developed. One goal in designing such machines is to achieve proper dowel bar placement in the new concrete while keeping manual labor and disturbance of the concrete to a minimum.
German Patent No. 3,117,544 issued to Vogele, for example, discloses a machine which forms recesses in the concrete and then buries the dowels with concrete. Unless the desired depth for the dowels is very shallow, this machine has to move a large volume of concrete in order to form the recesses and cover up the dowels. Disturbing so much concrete is inefficient and increases the likelihood of creating voids in the concrete or of displacing the dowels from their proper position in the concrete.
U.S. Pat. No. 4,433,936 issued to Moser and U.S. Pat. No. 4,799,495 issued to Laeuppi et al. disclose a horizontal frame of dowels with inserting guides or prongs positioned above the horizontal frame to drive the dowels downward through openings in the horizontal frame and into the concrete. By linking the horizontal frame of dowels and the inserting guides, the dowel insertion process is tightly restricted by the dowel feeding mechanism. A slight jam or mishap in feeding the dowels is likely to require stopping the machine, positioning some of the dowels by hand and attempting to smooth the concrete manually.
Another drawback is that dowel insertion devices are sometimes attached to the rear of a paving machine and the dowel insertion disturbs a graded, smoothed surface. Once the surface is disturbed by inserting the dowels, it must be smoothed again. Oscillating beams, sometimes used to smooth the surface after dowel insertion, cannot duplicate the paving job performed by the tube vibrator, tamping bar, extrusion pan and float pan of a paving machine.
The problem areas addressed by the present invention, therefore, relate to excessive disturbance of the concrete, difficulties in feeding dowels to the inserting mechanism, and the effort required to obtain a final, smooth concrete surface after dowel insertion.